Telephony is the technology of carrying voice between people over a network. For most of its history that meant the public switched telephone network (PSTN): copper wires, central office switches, and dedicated circuits for every call. Today it increasingly means VoIP, where voice travels as packets over the same IP networks as everything else, while still using phone numbers, dial tone, and handsets that behave much like they always have.
Sections¶
- History of the telephone: from Bell's 1876 patent through automatic switching, the digital network, dial-up modems, and the retirement of copper.
- VoIP: SIP providers, PBX software (Asterisk, FreePBX and alternatives), and running a phone system yourself.
- Hardware: telephones and adapters, including how to use a vintage rotary phone today.
Key terms¶
| Term | Meaning |
|---|---|
| PSTN | Public switched telephone network: the traditional circuit-switched phone network |
| POTS | Plain old telephone service: an analog copper landline |
| Central office (CO) | The phone company building where subscriber lines terminate and calls are switched |
| Pulse / DTMF | The two dialing methods: rotary loop interruptions, or Touch-Tone audio tone pairs |
| VoIP | Voice over IP: voice carried as packets on an IP network |
| SIP | Session Initiation Protocol: the standard protocol for setting up VoIP calls |
| PBX | Private branch exchange: a phone system that switches calls between internal extensions and outside lines |
| ATA | Analog telephone adapter: connects an ordinary phone to a VoIP service |
| DID | Direct inward dialing: a phone number that routes to a VoIP account or PBX |
| SIP trunk | A VoIP connection from a provider to a PBX, carrying one or more phone numbers |